calculting handicaps

Im trying to start a league at my local course. It is going to be a singles league but i do not know how to calculate handicaps. Can anyone help me out with this? Tips and how to's would be greatly appreciated.

We used to have a 3 week period to establish your handicap. After the 3 rounds are in, you take the average of the scores as the handicap. Every week after, you take the best 3 of the last 5 weeks and do the same.
When a new player comes in, until their handicap is established, they get a temporary handicap of the average round at the course for the last 3 weeks of all players at league.